Wireless networks have in recent years experienced a considerable increase in the amount of data being transmitted to and from wirelessly connected devices or user equipment, which includes mobile or cell phones (including so-called “smart phones”), personal digital assistants, pagers, tablet and laptop computers, content-consumption or generation devices (for music and/or video for example), data cards, or USB dongles, etc., as well as fixed or more static devices, such as personal computers, game consoles and other generally static entertainment devices, various other domestic and non-domestic machines and devices, etc. This increase in traffic has been mainly due to the rapid and widespread uptake of smart phones, the availability of mobile broadband dongles for computers and affordable rates for consumers.
The traffic characteristics of this data traffic are very different from that of traditional mobile phones, and can be characterized by its use of a lot of background signalling and bursty traffic consisting of relatively small data packets. The introduction of machine-type communications to the networks can also be expected to follow this trend. As a result, wireless networks need to implement new mechanisms to cope with this new traffic and make efficient use of the available resources while providing high capacity and throughputs and minimum delays. Of particular concern in improving the support of this low volume, bursty data is minimising the signalling load on the network and improving the power consumption of the user equipment.
The user equipment is typically in one of a number of predefined activity states. These may be for example an idle state, a paging state in which the user equipment checks the paging channel for incoming paging messages at predefined time intervals, and one or more data connection states in which the user equipment can actively transmit and receive data. In general, these states use increasingly more power at the user equipment and also more network signalling. One way to reduce power consumption and the amount of network signalling is to reduce the frequency with which the user equipment connects to the network, for example when looking for incoming control signals and/or data. However, this can limit how efficiently the user equipment can reselect other network cells and may even preclude some choices.
This can be exemplified by work currently being carried out on FE-FACH (Further Enhancement to CELL_FACH (Forward Access Channel)) for Release 11 of the 3rd Generation Partnership Project or 3GPP. The system currently in use provides for a number of defined activity states for the user equipment, including an Idle state, a CELL_PCH/URA_PCH (paging channel) state, a CELL_FACH (forward access channel) state, and a CELL_DCH (dedicated channel) state. In the Idle state, the user equipment does not have an RRC (Radio Resource Control) connection and is the state having the lowest power consumption. In the CELL_PCH/URAPCH state, the user equipment is again in a low power consumption state as it only intermittently looks for incoming paging messages, and in this state does have a RRC connection. However, the user equipment needs to be in the CELL_FACH or CELL_DCH state in order to be able to perform both transmission and reception of data (including in particular “user” data, as opposed to data relating to control or management of the device and its network connection, etc. for example). In the CELL_DCH state, a dedicated physical channel is allocated to the user equipment. In the CELL_FACH state, the user equipment shares the physical channel with other user equipment, though nevertheless may have a dedicated logical channel. As is well understood, a logical channel in this context is an information stream dedicated to the transfer of a specific type of information over the radio interface and corresponds to an individual signal which can be separated or isolated from an aggregate of signals which occupy the same physical bandwidth or channel CELL_FACH can be regarded as a transition state between the CELL_PCH/URA_PCH and CELL_DCH states. Keeping the user equipment in CELL_FACH state improves power consumption for the user equipment compared to the CELL_DCH state (because the transmitter and/or receiver may be switched off for longer periods of time while no uplink data is available and during discontinuous reception or “DRX”) and also reduces the network signalling load (by avoiding radio resource control or “RRC” signalling to perform a state transition from the PCH or Idle states to the CELL_FACH state when both data transmission and reception are required). Nevertheless, the CELL_FACH state still has a higher power consumption for the user equipment than the PCH or Idle states.
To address this, it has been proposed to introduce a longer, secondary DRX cycle in the CELL_FACH state. In particular, in the CELL_FACH state at present, the user equipment is only periodically receptive to incoming control signals from the network, including in particular the HS-DSCH High Speed Downlink Shared Channel signal, using a relatively short cycle period. It is proposed to use a second, longer cycle period if there has been no data activity for a predetermined period of time, which would reduce the power consumed by the user equipment. However, the measurement performance requirements for the user equipment in the CELL_FACH state mean that the mobility of the user equipment is less efficient than when in the CELL_PCH/URA_PCH state, i.e. the user equipment is somewhat restricted when it attempts to reselect a different network cell, which possibly uses a different protocol. Particular examples are that currently reselection to a cell using LTE (the “Long Term Evolution” standard) is not supported at all, and longer times may be needed to reselect within a UTRAN (“universal mobile telecommunications terrestrial radio access network”) system. This in turn means that a network operator typically would not want to keep user equipment in the CELL_FACH state for long periods of time, and therefore this proposal may have only a limited or minor benefit.